Pulp Paper & Logistics
XERIUM EUROPE 19
that – using a seam felt – the bottom felt has to sustain a lot of machine-direction tension without opening up at the seam area.
Calculations on seam yearns In the following calculations – based on a double-felted shoe press which is more critical compared to the single-felted shoe press with respect to the affecting loads – the importance of sufficient yarn anchorage and material strength is demonstrated. Due to the felt tension and the connection through the pintle wire, the forces on every seam loop are defined, as seen in Figure 4. The forces in place lead up to a situation as
follows: At the seam loop the sum of all loads is zero:
Figure 1: Seam felt market share trend in Europe
crescent former tissue machines, shoe presses on demanding graphical paper grades and high machine speeds are no longer exclusion criteria for using seam felts. Shoe presses have especially been a big challenge for Xerium’s R&D team, but also this mission has been completed successfully.
Show presses: a challenge for seam felts The specific requirements for the application of seam felts in shoe presses are – besides the marking freeness of the seam area – an absolute stability and durability of the seam structure itself. In the single-felted shoe press nip the press felt has to transmit the drive load from the
driven roll to the flexible shoe press belt and drag it along. This causes a significant tension difference between the press nip entrance and the nip exit in the felt. For endless felts this effect is not as critical due to their inherent structure. With regard to seam felts, the engineering and manufacturing techniques of the seam loops have been enhanced significantly to reduce these negative effects. This is illustrated in Fugure 2. The situation is even more demanding in a double-felted shoe press: The drive load is transmitted from the roll to the bottom felt which passes to the top felt and thereby turning the shoe press belt, as shown in Figure 3. Running such a configuration means
The forces which are effective at the seam loop are FL (Loop load coming from the felt tension) and the force FY (yarn anchorage):
The machine-dircetion (MD) yarn anchorage is measured in the laboratory and is defined as the load which is necessary to pull a 9.0 cm long MD yarn out of the press felt construction. The diagram in Figure 5 shows the pull-out forces of the design ProSeam SP in comparison to a standard seam felt design under wet conditions.
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Figure 2: ProSeam SP seam felt November 2013
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